1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine and a printer, that uses an electrophotographic system, and in particular to an image forming apparatus that is capable of forming a color image using a plurality of image bearing members and developing means that develop latent images formed on the image bearing members while contacting the image bearing members.
2. Related Background Art
As a conventional image forming apparatus that uses an electrophotographic process, there is a color image forming apparatus that adopts an in-line system (tandem system) in which a plurality of image forming portions are arranged in parallel and images are successively transferred onto a transferring material or the like on a transferring belt (intermediate transferring belt) or a transferring belt (transferring material transport belt) that is disposed so as to oppose the plurality of image forming portions. Here, each image forming portion includes an electrophotographic photosensitive member (photosensitive member) that is, for instance, a photosensitive drum. The image forming portion also includes process means, such as charging means, developing means, and cleaning means, that act on the photosensitive member.
As such a color image forming apparatus of the in-line system, there is a color image forming apparatus that has a construction where photosensitive members and process means, such as developing means, in respective image forming portions are integrally formed into process cartridges and these process cartridges are detachably attached to an image forming apparatus main body in a row. In accordance with this process cartridge system, when developer runs out, for instance, a user replaces the process cartridges by himself/herself without relying on a serviceman, thereby returning the image forming apparatus to a state where image formation is possible. At the same time, it is possible for the user to replace other consumable items such as the photosensitive members. Therefore, maintainability is greatly improved.
As developing means of each process cartridge applied to such an in-line type color image forming apparatus, there are generally known two systems that are a contact developing system, in which development is performed under a state where a developing roller is brought into contact with a photosensitive member, and a non-contact developing system in which development is performed under a state where a predetermined gap is formed between a developing roller and a photosensitive member. In the case of the contact developing system, however, there is a danger that there occur troubles given below.
(1) When photosensitive members rotate at a timing other than a developing operation (timing at which pre-rotation or post-rotation is performed, for instance), the surface layers of the photosensitive members are shaved due to rubbing with developing rollers, which becomes a factor of reduction of the service life thereof.
(2) At the time of mono-color development or the like, if cartridges for other colors that do not contribute to the development are also allowed to operate, the service life of their photosensitive members is greatly reduced.
(3) In the case where no bias is applied at the time of non-operation or during pre-rotation or post-rotation, developer on developing rollers adheres to photosensitive members, which becomes a factor of waste of the developer or stain on paper or the like due to the developer.
(4) In the case where an image forming apparatus remains unused for a long time under a state where process cartridges are attached to the main body of the image forming apparatus, the roller layers of developing rollers are permanently deformed, which becomes a factor of the occurrence of unevenness on an image at the time of development.
In order to solve the problems described above, there have been adopted various constructions. For instance, both of photosensitive drums and developing rollers for colors that do not contribute to image formation are retracted from a transferring belt and the driving of the photosensitive members and the developing rollers is stopped. Alternatively, a transferring belt is brought into contact with each photosensitive member for a required color by changing the traveling path of the transferring belt, and the driving of each photosensitive member and developing roller that do not contribute to image formation is stopped.
In the case of the conventional techniques described above, however, there is a disadvantage that a construction becomes complicated or there occurs a trouble due to the movement of the positions of photosensitive drums or the traveling path of a transferring belt that are important to the accuracy of image formation.
The present invention has been made in the light of the problems described above and an object of the present invention is to provide an image forming apparatus that is capable of suppressing reduction of the service life of an image bearing member.
Another object of the present invention is to provide an image forming apparatus that is capable of suppressing reduction of the service life of a developing roller.
Still another object of the present invention is to provide an image forming apparatus that facilitates switching between a full-color image forming state and a mono-color image forming state using a simple structure.
Still another object of the present invention is to provide an image forming apparatus including:
a plurality of image forming portions, each image forming portion including an image bearing member, developing means that is capable of contacting and being spaced from the image bearing member and supplies developer to the image bearing member, a motor that drives the developing means, and clutch means that is provided between the motor and the developing means;
a first switching means that acts on the plurality of clutch means; and
a second switching means for having the developing means contact and spaced from the image bearing member, the second switching means communicating with the first switching means and operating in association with an operation of the first switching means.
Still another object of the present invention is to provide an image forming apparatus including:
a first image forming portion for forming a black image, the first image forming portion including a first image bearing member and a first developing means that is capable of contacting and being spaced from the first image bearing member and supplies developer to the first image bearing member;
second image forming portions for forming images in colors other than black, each of the second image forming portions including a second image bearing member and a second developing means that is capable of contacting and being spaced from the second image bearing member and supplies developer to the second image bearing member; and
switching means for switching contact/space operations of the first developing means and the second developing means, the switching means being capable of moving the first developing means and the second developing means to a full-color image forming state in which the first developing means and the second developing means are respectively abutted against the first image bearing member and the second image bearing members, a mono-color image forming state in which only the first developing means is abutted against the first image bearing member, and a standby state in which all of the developing means are spaced from the image bearing members.
Still another object of the present invention is to provide a clutch applied to an image forming apparatus, including:
a gear portion that receives a power from a motor;
a drive side engagement component that receives the power transmitted to the gear portion; and
a driven side engagement component that receives the power from the drive side engagement component, the drive side engagement component and the driven side engagement component being capable of contacting and being spaced from each other,
in which the gear portion and engagement positions of the drive side engagement component and the driven side engagement component exist within approximately the same plane.
Other objects of the present invention will become apparent by reading the following detailed description with reference to the accompanying drawings.